Carbon dots-based red fluorescence nanoprobe for caspase-1 activity assay and living cell imaging

Abstract

The development of sensitive and convenient strategies for monitoring intracellular caspase-1 activity is of great significance. Herein, a novel fluorescence nanoprobe for caspase-1 activity determination was constructed based on surface energy transfer (SET) between red-emissive carbon dots (RCDs) as a donor, and Au nanorods (AuNRs) as an acceptor. The donor/acceptor pair were covalently bridged with a peptide containing a caspase-1 cleavage site (YVAD) at middle. The stability and dispersivity of the AuNR-Pep-RCD nanoprobe was realized/enhanced by pretreating the AuNRs with PEG-SH. Active caspase-1 cleaves the YVAD site, releasing RCDs and recovering the fluorescence. Synergic effect of the red-emission, sensitive and selective cleavage, and excellent SET efficiency contribute to the nanoprobe with high sensitivity and selectivity, especially in biological samples. More importantly, the nanoprobe can be uptaken by living cells, capable of in-situ intracellular caspase-1 activity imaging. The fluorescence recovery is linearly correlated with caspase-1 activity in the range of 5‒300 ng·mL−1 (2.5 × 10−5‒1.3 × 10−3 U·mL−1), with a limit of detection of 1.76 ng·mL−1 (8.8 × 10-6 U·mL−1). In particular, the fluorescence nanoprobe can accurately detect caspase-1 activity in cells extract, and sensitively probe the caspase-1 activation treatment and inhibition treatment for the intracellular caspase-1 activity levels.